This invention relates generally to a fuel injection pump of the distribution type, and more particularly to an improvement in the operation of a load timer for adjusting the fuel injection timing.
Japanese Laid-Open (Kokai) Patent Application No. 119132/82 discloses a fuel injection pump of the distribution type. This fuel injection pump is provided with a housing 2 whose internal space serves as a pump chamber. A drive shaft 6 to which the rotation of an engine is transmitted extends into the housing 2. One end portion of the drive shaft 6 disposed within the pump chamber is connected to one end of a plunger 5 through a coupling so as to rotate the plunger 5 in a manner to allow an axial movement of the plunger 5. The other end of the plunger 5 cooperates with the housing to form a fuel pressurizing chamber 14. The rotational movement of the plunger 5 serves to distribute the fuel in the fuel pressurizing chamber sequentially to a plurality of injection nozzles. Cam mechanisms 7 and 8 for reciprocally moving the plunger 5 axially in response to the rotational movement of the plunger 5 are provided within the pump chamber. When the plunger 5 moves in one direction (that is, at a suction stroke), it draws the fuel into the fuel pressurizing chamber 14, and when the plunger 5 moves in the other direction (that is, at a pumping stroke), it pressurizes the fuel in the fuel pressurizing chamber 14.
A control sleeve 19 is axially slidably mounted on the outer periphery of the plunger 5. A cut-off port 31 in the plunger 5 is closed by the control sleeve 19 during the pumping stroke, and when the cut-off port 31 moves away from the control sleeve 19, the pressurized fuel in the fuel pressurizing chamber 14 escapes to the pump chamber via the cut-off port 31, thus finishing the fuel injection. The position of the control sleeve 19 determines the amount of injection of the fuel. A lever assembly is pivotally supported within the housing 2. The position of the control sleeve 19 and hence the fuel injection amount are adjusted by this lever assembly. A governor spring 41 for receiving an operating force of an accelerator pedal is accommodated within the housing 2. The governor spring 41 urges the lever assembly to be pivotally moved so as to move the control sleeve 19 in the direction of the pumping stroke of the plunger 5, that is, so as to increase the fuel injection amount. A governor is also received within the housing 2. This governor urges the lever assembly to be pivotally moved so as to move the control sleeve 19 in the direction of the suction stroke of the plunger 5, that is, so as to decrease the fuel injection amount. This governor comprises a governor shaft 45 fixedly mounted on the housing 2 and extending into the pump chamber, a governor sleeve 37 axially slidably mounted on the outer periphery of the governor shaft 45, a rotation member 46 mounted on the governor shaft 45 so as to be rotated by the rotation of the drive shaft 6, and fly weights 47 supported on the rotation member 46. Under the influence of the centrifugal force of the fly weights 47 caused by the rotation of the rotation member 46, the governor sleeve 37 urges the lever assembly to be pivotally moved.
A main timer 39 is provided on the housing 2. The main timer 39 adjusts the above cam mechanisms 7 and 8 in accordance with the pressure in the pump chamber so as to adjust the fuel injection timing. This adjustment is made in such a manner that the higher the pressure in the pump chamber is, the earlier the fuel injection timing is.
The fuel injection pump of the above prior publication is also provided with a load timer which cooperates with the main timer 39 to adjust the fuel injection timing in accordance with the load of the engine. This load timer includes the above-mentioned governor. The load timer further includes a relief hole 49 formed in the governor shaft 45 and extending axially thereof, a first communication passage passing through the peripheral wall of the governor shaft 45 surrounding the relief hole 49, and a second communication passage passing through the peripheral wall of the governor sleeve 37. The first communication passage has a single annular groove 48 formed in the outer peripheral surface of the governor shaft 45, and a port communicating the annular groove 48 with the relief hole 49. The second communication passage is defined by a single control hole 50 of a small cross-sectional area.
The above load timer is of a well-known construction. In this load timer, when the engine load is low, the governor sleeve 37 is positioned forwardly, and therefore the control hole 50 is in communication with the annular groove 48, so that the pressure in the pump chamber escapes to the relief hole 49. The area of communication between the control hole 50 and the annular groove 48 is equal to the total cross-sectional area of the annular groove 48, and therefore the pressure in the pump chamber is at the minimum level, so that the fuel injection timing determined by the main timer is the latest. As the engine load increases, the governor sleeve 37 is gradually retracted, and therefore the area of communication between the control hole 50 and the annular groove 48 is gradually decreased, so that the pressure in the pump chamber increases, and therefore the fuel injection timing becomes earlier or advanced. When the engine load further increases, so that the governor sleeve 37 is retracted, the control hole 50 is closed by the governor shaft 45, and therefore the pressure in the pump chamber is increased, so that the fuel injection timing becomes the earliest.
In the above known load timer, during the idling of the engine immediately after the start of the engine at cold places or high places, the fuel injection timing is late or delayed because of a low engine load, and therefore the engine may be stopped or may produce smoke. To deal with such difficulty, the fuel injection pump of the above prior publication is provided with a solenoid valve 51 for opening and closing the relief hole 49, and a control unit 52 for controlling the solenoid valve 51. The control unit 52 controls the solenoid valve 51 in accordance with information (e.g. the temperature of cooling water for the engine, the atmospheric pressure, the engine load, and so on) inputted thereto, so that the fuel injection timing can be advanced or made earlier even during a low-load operation of the engine and even at a low atmospheric pressure. However, because of the addition of the solenoid valve 51 and the associated control circuit, the cost involved is increased.
A fuel injection pump of the distribution type disclosed in Japanese Utility Model Publication No. 8674/89 (FIGS. 3 and 4) is provided with an atmospheric pressure compensation mechanism which decreases a fuel injection amount and advances a fuel injection timing when the atmospheric pressure is low. This atmospheric pressure compensation mechanism includes a bellows 32 which is axially expanded and contracted in accordance with the atmospheric pressure. An upper end of an adjust pin 35 is connected to the lower end portion of the bellows 32. The adjust pin 35 has a tapered surface 35a, and is supported on a housing so as to slide axially in a vertical direction. The adjust pin 35 moves downward as the bellows 32 expands. A sensor pin 36, extending in a direction perpendicular to the adjust pin 35, is also supported on the housing so as to slide axially. One end of the sensor pin 36 is in contact with the tapered surface 35a of the adjust pin 35 whereas the other end thereof is disposed within a pump chamber. A link 25 is pivotally supported on the housing, and an upper end of the link 25 is in contact with the other end of the sensor pin 36. When the engine is under a full load, a tension lever 24 of a lever assembly is abutted at its upper end against the lower end of the link 25 to limit the fuel injection amount. When the atmospheric pressure is low, the bellows 32 is axially expanded to move the adjust pin 35 downward, so that the link 25 is pivotally moved through the sensor pin 36. As a result, the tension lever 24 is kept at a small inclination angle by the lower end of the link 25, thereby decreasing the fuel injection amount in the full load condition of the engine. An auxiliary timer 40 is provided on the housing. The auxiliary timer 40 comprises a guide sleeve 41 fixedly mounted on the housing, and a valve member 43 received in the guide sleeve 41 for sliding movement therealong. The valve member 43 is coaxial with the sensor pin 36. The valve member 43 has a relief hole 43a extending axially thereof. One end of the relief hole 43a is communicated with the pump chamber, and the other end thereof is communicated with an annular groove 43b, formed in the outer periphery of the valve member 43, via a through hole 43c. A through hole 41f is formed in the guide sleeve 41, and the amount of relief of the fuel from the pump chamber is determined in accordance with the area of communication between the through hole 41f and the annular groove 43b. The valve member 43 is urged by a spring 44 to be contacted at its distal end with the sensor pin 36 through the upper end of the link 25. when the vehicle is at a low place where the atmospheric pressure is high, the area of communication between the through hole 41f and the annular groove 43 is large, and the pressure of the pump chamber is low. Therefore, the fuel injection timing is set by a main timer to a delayed timing. When the vehicle is at a high place where the atmospheric pressure is low, the bellows 32 is expanded to move the adjust pin 35 downward, so that the sensor pin 36 retracts the valve member 43 through the link 25, thereby decreasing the area of communication between the through hole 41f and the annular groove 43b to increase the pressure of the pump chamber. As a result, the fuel injection timing becomes earlier.
However, in the fuel injection pump of the distribution type disclosed in the above Japanese Utility Model Publication No. 8674/89, since the auxiliary timer 40 separate from the governor is required, the construction is complicated, and the cost is high. Further, the auxiliary timer 40 can not adjust the fuel injection timing in accordance with the load.
Japanese Laid-Open Patent Application No. 37572/80 discloses an atmospheric pressure compensation mechanism similar to that disclosed in the above Japanese Utility Model Publication No. 8674/89. This atmospheric pressure compensation mechanism adjusts the amount of pivotal movement of a collector lever 30 in accordance with the atmospheric pressure, thereby decreasing the fuel injection amount when the atmospheric pressure is low. However, this atmospheric pressure compensation mechanism is not designed to adjust the fuel injection timing in accordance with the atmospheric pressure.